I purchased on March 7 the New International Commentary on the New Testament (21 volumes) set. When I downloaded it, I got two "tools" listed in my library: NICNT (18 vols.) and NICNT (3 updated vols.).

I was continuing my addictive habit of browsing the Accordance store and noticed that there was an upgrade (http://www.accordanc...=NICNT21upNICNT). When I clicked on it I see the following written on the top:

This upgrade is available to users who previously purchased the 20-volume New International Commentary on the New Testament (NICNT). Purchase of this upgrade will supply the user with the 21-volume NICNT (NICNT (21volumes)) which adds the 2nd volume of Hebrews (NICNT2-Hebrews).

To get full functionality with the new 21-volume NICNT, users should remove the original NICNT module from the Accordance Library prior to upgrading to the new NICNT (21volumes) module.

So, I realize that 18 + 3 is 21. My questions are, though:
1) Do I have it correctly in my library, or should it be a unified library item (such as NICNT 21 vols)?
2) Do I need the upgrade that I have linked above, or do I already have it? As a follow up, is it possible to list the release date of items in the store, or how is it best to know if an upgrade applies to your current library items?

Yes, you have it correctly in your library (i.e., split up like that). And March 4 or 5, I believe, was the day the upgrade was available, so it sounds like you already have it if you purchased the whole series after that.

The new Hebrews volume is by Cockerill, so you could always double-check your NICNT for that volume, but if you have 21 volumes, it's there. "NICNT2-3" is the name of the little module that has the new Hebrews volume.

If you're ever unsure about whether you have something or not, you can add it to your cart, and then your shopping cart will tell you something like, "Our records indicate you already own this item." I'm not sure how well that works with upgrades (or if it does), but presumably if you added the upgrade to your cart, it would tell you you already have it.

BTW, you can sort store pages by most recent. I have new "English Studies" releases, for example, bookmarked at this link, which shows the most recent at the top. It doesn't give you dates in the way you're asking for, but it's a good way to stay on top of anything new that comes out. I have a similar bookmark for Greek and Hebrew releases. I probably check these at least once a week. Okay--maybe two or three times.